1. Field of the Invention
This invention relates to a locknut system, that is to say a system for preventing the inadvertent release of a nut from a threaded member of which the nut is mounted.
2. The Prior Art
Nuts, screw threadedly mounted on a projecting screw threaded members (which may for example be studs, bolts or screws) are commonly used as mechanical fastenings. Such combinations (which for convenience are hereinafter referred to as “a nut and bolt”) have well recognised advantages as mechanical fastenings. Equally, it is well recognised that unless special precautions are taken to prevent inadvertent slackening off of the nut, nut and bolt fastenings are liable to fail as a result of slackening off of the nut, especially where the nut and bolt are used in applications where they are dynamically loaded. A typical example of such a problem is on the wheel nuts used to retain vehicle wheels, especially on buses and trucks. The dynamic loading of the nuts and wheel studs in such applications can lead to unintended slackening of the nut with possible catastrophic results if a wheel becomes completely detached. For this reason, a number of arrangements have been proposed for preventing such unintended slackening off of the nuts which retain road wheels in position. The present invention provides in its preferred embodiment a simple system for preventing the unintended release of wheel nuts from vehicles, but it is to be understood that the invention is not limited to such applications but rather is applicable to all circumstances where the unintended release of a nut from a screw threaded member is to be avoided.
According to a first aspect of the present invention there is provided a locknut system comprising a projecting screw threaded member having a first thread, the first thread being an external thread; a nut for mounting on the projecting screw threaded member, the nut having a thread for co-operating with the first thread of the screw threaded member; a second screw thread on the projecting screw threaded member, the second screw thread being of different hand and/or being of different pitch from the first screw thread; a locking member having a screw thread for engagement with the second screw thread of the projecting screw threaded member and having an engaging surface which can be brought into abutting contact with a corresponding engaging surface on the nut by mating the thread of the locking member with the second thread of the projecting screw threaded member; and a coupling member for coupling the locking member and the nut to substantially prevent relative rotation there between, wherein one of the locking member and the coupling member carries a snap ring which snaps into engagement with a retaining recess provided on the other of the coupling and the locking member when the coupling member is mounted in its use configuration, to prevent accidental displacement of the coupling member from the locking member.
In the preferred embodiment of the present invention the second thread is of opposite hand to the first thread and is formed in a bore provided extending from the end of the projecting screw threaded member. Accordingly, the screw-threaded part of the locking member is in the form of a projection which may be screwed into the second thread. Preferably, the engaging surface of the locking member is provided as a skirt which depends from a flange connected to the screw threaded part of the locking member. Preferably, the external profile of the peripheral edge of the locking member is multi-faceted, for example hexagonal or multi-hexagonal. Preferably, the snap ring is located in a groove in the outer peripheral surface of the locking member.
Preferably, the coupling member is in the form of a cap which is formed with a profile whereby it can be mounted on the nut in a manner that prevents relative rotation between the nut and the cap. Preferably, the cap also includes a profile which can engage the locking member to prevent relative rotation between the locking member and the cap. Preferably, the same profile on the cap engages both the nut and the locking member. Preferably, the profile is a multi-hexagonal profile.
Preferably, the snap ring is of metal, for example, spring steel.